Beam homogenizer

ABSTRACT

A system for homogenizing the intensity profile of light includes a plurality of fiber coupled light sources for emitting fiber output beams from fiber output ends, and a light pipe optically coupled to the fiber output beams for producing a uniform light pipe output beam, an interleaver that transmits a first set of fiber output beams and reflects a second set of fiber output beams so that the principal rays of the fiber output beams propagate in a common plane, a first optical element for converging the principal rays, and a second optical element for telecentrically imaging the beams into the light pipe such that the principal rays of the beams propagate parallel to each other and the beams are focused in the light pipe in a focal plane transverse to the direction of propagation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Generally, the field of the present invention is beam homogenizers. Moreparticularly, the present invention relates to the homogenization offiber coupled light sources.

2. Background Art

Advances in semiconductor lasers permit manufacturers to offerincreasingly higher laser powers at a variety of wavelengths for a widevariety of applications. Typical applications of semiconductor lasersinclude materials processing (cutting and scribing materials),communications systems, medical devices, lighting, and analyticalinstrumentation. In many applications, to provide even higher opticalpowers, outputs from multiple devices are combined using combinations oflenses, mirrors, bulk beamsplitters, and fused fiber couplers. In manycases, laser beams produced by semiconductor lasers are not circular butelliptical, and typically have differing beam waists based on theelongated shape of the laser emission area.

Some applications impose difficult requirements on beam uniformity.While considerable effort has been directed to combining laser outputsto produce uniform beams, the available systems nevertheless continue toexhibit some significant limitations. Complex, expensive arrangements ofnumerous optical elements can be needed, and such elements can requireprecise, stable alignment to produce an acceptable combined beam.

Thus, despite the considerable efforts that have been exerted for manyyears, there remains a long felt need for laser beam combining systemsthat provide highly uniform combined optical beams.

SUMMARY OF THE INVENTION

Irradiation systems include a plurality of fiber coupled light sources,each source configured to produce corresponding beams propagating alongrespective propagation axes that are situated in a common direction suchas a common plane and in relation to an optical axis. The radiationbeams are displaced with respect to each other and are incident to aconverging optical element situated along the optical axis that directsthe beams toward the optical axis. The converging optical element can bea refractive, reflective, or other optical element having a positiveoptical power. In some examples, the converging element is a cylindricalmirror or lens. The irradiation systems also include a lens situated toreceive the radiation beams from the converging optical element and formcorresponding beam foci that are displaced with respect to each other ina direction perpendicular to the optical axis and in the common plane. Alight pipe is situated to receive the focused beams and multiply reflectthe focused beams to a light pipe output so as to form an output beam.The output beam is typically a homogenized beam having an intensityuniformity of better than at least 10% along at least one axis.

In some examples, each of the fiber coupled light sources includes atleast two laser diodes coupled to a multimode optical fiber. In otherexamples, the converging optical element is a cylindrically convergingoptical element and the beam foci are line foci extendingperpendicularly to the common plane. In further examples, the light pipeincludes a solid transparent substrate that defines a propagation volumehaving a rectangular cross section of width W and height H. In otherexamples, the light pipe includes a frontal surface of height Hconfigured to receive the focused beams, and at least two exteriorsurfaces configured to direct the multiply reflected input beams from aninput portion of the frontal surface to an output portion of the frontalsurface so as to produce an output radiation flux. In additionalrepresentative embodiments, a beam processing lens is configured toproduce a process beam based on the output radiation flux from theoutput portion of the frontal surface and direct the process beam to awork surface. In typical examples, the input portion and the outputportion of the light pipe frontal surface are rectangular, and theprocess lens is configured to produce a rectangular illumination beam atthe work surface. In some examples, the light pipe is situated so as tomultiply reflect the focused beams based on focused beam numericalaperture in the common plane.

Methods of producing homogenized optical beams include receiving aplurality of optical beams propagating at different angles with respectto an axis. Each of the plurality of beams is directed towards the axisand the received beams are processed so as to increase beam numericalaperture in at least one direction. The processing beams are directedinto a light pipe so as to produce an output beam. In some examples,each of the plurality of beams propagates in a common plane and isdirected towards the axis in the common plane. In further representativeexamples, each of the plurality of beams has an initial beam numericalaperture in at least one direction and is processed so that the outputnumerical aperture in the at least one direction is at least 5 times theinitial input beam numerical aperture. In additional representativeexamples, the light pipe is selected so that the processed beams aremultiply reflected in the light pipe in a direction associated with theincreased beam numerical aperture. In still other examples, beamnumerical apertures are increased in the common plane, and the lightpipe is selected to multiply reflect at surfaces perpendicular to thecommon plane. In other examples, the light pipe is selected so as tohave surfaces parallel to the common plane and is situated so that theprocessed beams propagate within the light pipe without multiplereflection by these surfaces.

Apparatus for producing uniform optical beams include a convergingoptical element configured to receive a plurality of optical beams, eachof the beams having an initial beam numerical aperture. A lens issituated to receive converging optical beams from the converging opticalelement, and is configured to increase the numerical aperture of each ofthe beams in at least one direction. A light pipe is configured toreceive the increased numerical aperture beams, and multiply reflect thereceived beams to a light pipe output surface. In further embodiments,the lens is configured to increase the beam numerical aperture along afirst beam cross-sectional axis, and the light pipe includes opposingsurfaces perpendicular to the first beam cross-sectional axis so as tomultiply reflect the received beam to the light pipe output surface. Inother representative examples, a beam interleaver is configured toreceive beams from a first plurality of beams propagating along a firstaxis and a second plurality of beams propagating along a second axis,and direct the beams of the first and second pluralities of beams so asto propagate along a common axis toward the converging optical element.In additional embodiments, the interleaver is configured to direct thebeams so that the beams are adjacent as propagating to the convergingoptical element. In other examples, the beams are multiply reflected soas to irradiate a rectangular area of the output surface, and a lens isprovided to direct a rectangular output beam to a work surface based onthe irradiated rectangular area.

The foregoing and other objects, features, and advantages will becomemore apparent from the following detailed description, which proceedswith reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C respectively are perspective, plan and side illustrations ofa representative illumination system in which beams from a plurality ofsources are combined and homogenized in a light pipe.

FIGS. 2A-2B respectively are plan and perspective illustrations of abeam interleaver.

FIGS. 3A-3B respectively are perspective and plan illustrations of a rodlens such as used in the system of FIGS. 1A-1C.

FIGS. 4A-4B respectively are plan and perspective illustrations of afolded light pipe such as used in the system of FIGS. 1A-1C.

FIG. 5A schematically illustrates operation of the optical system ofFIGS. 1A-1C.

FIGS. 5B-5C schematically illustrate ray propagation of selected beamsin the optical system of FIG. 5A.

FIG. 6 is a block diagram of a system for exposing a work piece topatterns defined on a mask.

FIG. 7 is a perspective illustration of a beam interleaver.

FIG. 8 is a schematic illustration of another illumination systemalternative to that of FIGS. 1A-1C.

FIG. 9 is an alternative view of the illumination system of FIG. 8.

FIG. 10 is a schematic illustration of a system for mounting to agantry.

DETAILED DESCRIPTION OF THE INVENTION

As used in this application and in the claims, the singular forms “a,”“an,” and “the” include the plural forms unless the context clearlydictates otherwise. Additionally, the term “includes” means “comprises.”Further, the term “coupled” does not exclude the presence ofintermediate elements between the coupled items.

As used herein, an optical flux refers to propagating optical radiationin a wavelength range of between about 300 nm and 2000 nm, and typicallybetween about 700 nm and 1600 nm. Typically, such optical fluxes can bepropagated in solid optical waveguides such as optical fibers that aresilica-based. However, in other examples, longer or shorter wavelengthscan be used, and waveguides such as fibers can be made of othermaterials as appropriate. In addition, in convenient examples, anoptical flux provided to a fiber or other waveguide can be produced by alaser or other source that can produce a spatially coherent flux, butlight emitting diodes or other sources can be used, and input opticalfluxes need not be spatially coherent. As used herein, devices andsystems that produce radiation at wavelengths between about 300 nm and2000 nm are referred to as illumination system or irradiation systems.

In some examples, optical beams or other optical fluxes and waveguidessuch as optical fibers are referred to as extending along an axis oralong an optical axis or common direction or common plane. Such axes,directions, and planes are not necessarily straight, but can be bent,folded, curved, or otherwise shaped by optical elements such as mirrors,lenses, or prisms, or due to the flexibility of a waveguide such as anoptical fiber. Optical beams propagating along an axis are associatedwith a distribution of propagation angles with respect to the axis. Forconvenience in the following description, an optical beam is referred toas having a beam numerical aperture that is the sine of one half of abeam divergence angle. Beam divergence can be based on angles associatedwith beam intensity relative to a central maximum of 95%, 75%, 50%, 1/e²or other convenient relative magnitude. For asymmetric beams, twodifferent beam numerical apertures can be used to describe beampropagation as the cross-section of such beams expands or contractsdifferently in different directions.

According to some examples, beam uniformity of better than 10%, 5%, 4%,2%, or 1% is provided. As used herein, relative beam uniformity isdefined as (I_(max)-I_(min))/I_(avg), wherein I_(max) is a beam maximumintensity, I_(min) is a beam minimum intensity, and I_(avg) is anaverage beam intensity. Typically, focused beams from laser diode barshave been used to work surfaces. However, the output from laser diodebars does not exhibit the intensity uniformity desirable for effectivelaser application. For example, each of the laser diodes in the bar mayemit a different power distribution, and the spacing between the diodesin the bar limits the uniformity of the output beam as well. Moreover,should a particular diode fail in a laser bar the uniformity of theoutput beam is also adversely affected.

With reference to FIGS. 1A-1C, a representative illumination system 100includes first and second linear arrays 102, 104 of fiber-coupledradiation sources 102 a-102 k, 104 a-104 k, respectively. The lineararrays 102, 104 include a plurality of fiber output ends that terminateoptical fibers 112, the fibers having laser diode radiation coupled intofiber input ends thereof. Optical fibers having core diameters of about200 μm and numerical apertures of about 0.1 are suitable. In someexamples, each fiber output end is associated with radiation coupledinto a corresponding input end from a single laser diode or multiplelaser diodes 114. Schulte et al., U.S. Pat. No. 7,443,895 that isincorporated herein by reference describes representative laser diodearrangements that can be used to couple radiation from multiple laserdiodes into a single fiber. Typically, the fiber-coupled radiationsources are nominally identical (radiation wavelength and range, powerrange, beam size and numerical aperture), but radiation sources can beindividually selected as needed. One or more of the radiation sourcescan be intensity or frequency modulated as well, and a visiblewavelength radiation source can be provided to aid in visual alignment.

While the linear arrays 102, 104 can be configured to provide circularlysymmetric fiber output beams 109, cylindrical beams can also be producedthat have different beam widths and divergence angles along differentcross-sectional axes. Suitable beam forming optics coupled to theoptical fiber 112 or situated between the fiber output end thereof andan interleaver 110, or elsewhere in the beam path, can include sphericaland cylindrical lenses (of regular or irregular curvature), gradientindex lenses, Fresnel lenses, holographic optical elements, prism-basedanamorphic optical elements, and other beam forming optics asconvenient. Optical fibers 112 used to deliver optical radiation to suchbeam forming optics can be single mode fibers or multimode fibers, andfiber core diameter and numerical aperture can be selected asconvenient. In some embodiments, arrays 102, 104 have a non-lineararrangement such as a rectangular configuration, as will be discussedinfra, and may include singular arrays of elements as well.

As shown in FIGS. 1A-1C, the arrays 102, 104 are arranged so that theoutput beams 109 have principal rays 117 emitting parallel and spacedapart from each other and in a particular associated direction for eacharray. Optical beams 109 from each of the fiber coupled light sourcesare directed to the beam interleaver 110 that is configured to reflectradiation from the fiber coupled sources 102 a-102 k and transmitradiation from the fiber coupled sources 104 a-104 k into a generallycommon direction or plane relative to an optical axis 105 and towards acylindrical concave mirror 120. As shown, the principal rays 117propagate in a generally planar direction throughout the system 100.However, in other embodiments the principal rays 117 may be arranged inanother configuration, such as a rectangle, such that rays propagatethroughout in a configuration other than planar. Moreover, rays 117 maybe arranged so that propagation after the fiber output ends occurs alonga convergent or divergent direction.

Again referring to FIGS. 1A-1C, for convenience, only propagation axes106, 107 associated with the fiber sources 102 a, 104 k are shown,however an optical axis 105 is shown generally at various partsthroughout the system 100. The beams can be circular, elliptical or haveother cross-sectional shapes and can have different beam divergences indifferent directions. Typically, the beams reflected and transmitted bythe interleaver 110 are approximately collimated, and beam diameters donot increase or decrease by more than a factor of about 1.5 overpropagation distances of up to about 500 mm. Beams in arrays 102, 104also may be directly coupled into the light pipe 140 without thepresence of intermediate optics. In one embodiment, the fiber outputends have a wedge shape (not shown) effectively increasing thedivergence angle of light emitted with respect to an axis perpendicularto the wedge and propagation direction, such as for example propagationaxis 106. With the diverging beam coupled into the light pipe 130, lightis multiply reflected off the interior walls thereof. The light pipe cantherefore be made shorter so as to make the apparatus more compact.

As shown in FIGS. 1A-1C, the concave mirror 120 directs and convergesthe beams to a cylindrical lens 130 that can be implemented as a sectionof a glass, fused silica, a crystalline material, transmissive plastic,or other material. The cylindrical lens 130 directs the beam into alight pipe 140 at a frontal surface 142 thereof such that opticalradiation from the beams is mixed and scrambled via reflection offinterior walls or surfaces through a propagation region 144 therein inorder to form a uniformly irradiated area 142 at an output surface 143of the light pipe 140. Consequently, the output beam 148 of the lightpipe 140 has a uniform intensity distribution across at least one axistransverse to the direction of propagation.

The light pipe 140 is conveniently formed of glass, plastic, or othermaterial that is transmissive with respect to the optical beams. To makethe optical system 100 more compact, a radiation propagation region 144within the light pipe 140 can be folded as shown using light pipesurface 146, 147 that causes the output beam 148 to propagate in adirection opposite to that of the input beams. Additional surfaces maybe added to reflect the output beam 148 into a different directionincluding the same or a parallel direction as the input beams. In someembodiments the propagation region 144 may also be a hollow cavityfilled with air or another suitable propagation medium. In otherembodiments, the light pipe 140 is formed of different materials suchthat the combination has a varying index of refraction within and suchthat light propagating through is reflected on a small scale. The smallreflections further homogenize the beam 148 at the output of the lightpipe 140.

A beam conditioning optical system 150 includes a first lens assembly152 and a second lens assembly 154 that produce a processed optical beambased on radiation received from the area 142. Typically, the processedoptical beam is transmitted through a protective window 160 to a worksurface. The protective window 160 is generally part of a suitablehousing 162, shown in FIG. 6, that contains the remainder of the opticalsystem 100 and serves to protect optical components from damage andexposure to contamination as well as prevent unnecessary user contactthat could result in misalignment or beam exposure.

FIGS. 2A-2B illustrate a representative beam interleaver 200 that can beused in the system of FIGS. 1A-1C. The interleaver 200 comprises atransmissive substrate 202 such as quartz or glass that is provided witha plurality of reflective coated areas 204 and a plurality oftransmissive areas 206. The reflective areas 204 can include a metallicreflective coating and/or a multilayer coating (such as a dielectriccoating) selected to provide substantial reflectivity at one or morewavelengths at which radiation is to be received. As used herein, asubstantial reflectivity refers to a reflectivity that is at least about90%, 95%, 99%, or higher. The reflective coatings can be selected basedon radiation polarization, input beam numerical aperture andcross-sectional dimensions as well. As shown in FIG. 2A, the reflectivecoated areas 204 are rectangular, but in other examples, these areas arecircular, elliptical, oval, square, polyhedral or other shapes thatpermit efficient transmission and reflection of beams. Anti-reflectivecoatings can be applied to the transmissive area 206. Although theinterleaver 200 can be situated so as to receive beams for transmissionand reflection at a 45 degree angle of incidence, other angles ofincidence can be used, and coatings suited to these angles used.Although in many applications, the interleaver 200 is intended for usewith a plurality of sources at the same wavelength, one or more of thereflective coated areas 204 or the transmissive areas 206 can beprovided with coatings suitable for different wavelengths orpolarizations. While solid transmissive substrates can be used, asubstrate that includes apertures situated to transmit select beams andhaving surface areas that are reflective can also be used. In addition,reflective or antireflective coatings can be applied on either surfaceof a solid substrate, and it can be advantageous to cover one surfacewith an anti-reflection coating while an opposing surface includesalternating anti-reflection coated and high reflectivity coated areas.

FIGS. 3A-3B illustrate a representative rod lens 300 that includes flatsurfaces 302, 304 that can be used for convenient mounting, andcylindrically curved surfaces 306, 308. In use, only a portion of therod lens 300 receives an optical flux, and a representative irradiatedarea 310 is illustrated. Curvatures of the surfaces 306, 308 can besubstantially the same so as to form a symmetric biconvex cylindricallens, but the curvatures of these surfaces can vary in sign andmagnitude, and cylindrical or acylindrical or other curvatures or flatsurfaces can be used.

A representative folded light pipe 400 is illustrated in FIGS. 4A-4B.The light pipe 400 includes a transmissive substrate 401 having aninput/output surface 402. An input portion 403 of the surface 402configured to receive an optical flux and transmit the flux into theinterior of the substrate 401. The light pipe 400 is arranged so that aflux perpendicularly incident to the surface 402 and centered in theinput area 403 propagates along an axis 405 that is folded by surfaces404, 406 and extends to a center of an output area 413 of the surface402. With reference to orthogonal coordinate axes xyz, an input beam orbeams that are substantially divergent along a y-direction experiencemultiple internal reflections within the light pipe 402 between oppositeinterior surfaces or walls 407, thereby promoting beam uniformity. Ifthe input beam is collimated along an x-direction, the input beampropagates without substantial beam spreading. As a result, the inputbeam propagates through the light pipe 400 in volume 408 and becomesappreciably more uniform in intensity across the y-axis. It will beappreciated that the volume 408 and the light pipe 400 need not befolded as shown and can be arranged so that an input beam propagatesalong an unfolded optical axis. Alternatively, other folds, combinationsof folds, or not folds can be used. Folds that provide beam reflectionsbased on total internal reflection are generally preferred, but externalreflective coatings can be used. Light pipes are conveniently formed ofsolid transmissive materials, but spaced apart reflective surfaces suchas mirrors can be used.

The operation of the optical system of FIGS. 1A-1C is illustrated withreference to FIG. 5A. Outermost optical beams from radiation sources 102a, 104 k are reflected by the concave cylindrical mirror 120 so as topropagate along axes 506 a, 508 a as beams 506, 508, respectively.Although the system of FIGS. 1A-1C provides 24 such beams, for clarityof illustration, other beams are omitted from FIG. 5A. The beams 506,508 are approximately collimated and the axes 506 a, 508 a subtend anangle θ with respect to an optical axis 512 that is perpendicular to thefrontal surface 142. The rod lens 130 receives the collimated beams 506,508 and directs beam principal rays 506 a, 508 a along ray directionsthat are approximately parallel. Ray directions that have been omittedfor clarity of illustration are also directed to become approximatelyparallel to each other. Additional focused lines from the other omittedbeams are not shown for clarity. The separation of the beams 512 a, 514k is selected based on the height H as well as the power of the incomingbeams and the adjacent distance between each. Typically, the frontalsurface 142 is situated so that the incoming beams are substantiallycaptured by the light pipe.

FIG. 5B illustrates propagation of representative central rays(principal rays) and marginal rays from selected beams to the lens 130and the light pipe entrance surface 142 in an exemplary embodiment.Outermost beam 506 as well as an intermediate beam 510 are illustrated.Because beam 506 is approximately collimated after reflection off themirror 120 but before entering the rod lens 130, the associated outermarginal ray 506 b and inner marginal ray 506 c propagate approximatelyparallel to the principal ray 506 a. The associated principal andmarginal rays 510 a-c for beam 510 propagate similarly. Therepresentative beams 506, 510 intersect at a projection window 514, orvirtual aperture, positioned before the rod lens 130. After refractingthrough the rod lens 130, principal rays 506 a, 510 a of beams 506, 510propagate telecentrically towards and in through the surface 142 of thelight pipe 140 so as to be roughly or substantially parallel to eachother. Due to lens 130, the respective marginal rays, for example rays506 b, 506 c, converge to a focus approximately in focal plane 518.Focal plane 518 may also be curved or have other shapes depending on therod lens 130 and the characteristics of the beams incident therein. Dueto the divergence of the beams after the focal plane 518, the beams 506,510 multiply reflect off the interior surfaces of the light pipe 140 soas to produce a homogenized downstream intensity profile, particularlyat the exit thereof such as at the output area 413 (see FIG. 4A). Asshown, this multiple reflection occurs in the y-dimension, however inother embodiments the homogenization may occur in multiple dimensions.

FIG. 5C illustrates ray propagation of beams 506, 510 in an alternativeembodiment. Other beams are not shown for clarity. Beams 506, 510 andassociated respective principal and marginal rays 506 a-c, 510 a-cconverge to a focus 516 approximately intersecting each other along axis512. Beams 506, 510 refract through rod lens 130 with the principal rays506 a, 510 a thereof propagating roughly or substantially parallel toeach other. The beams then diverge so that marginal rays multiplyreflect off the interior surfaces of the light pipe 140 so as to producea similarly homogenized downstream optical intensity profile at theoutput of the light pipe 140. Similar to other embodiments describedherein, because the beams 506, 510 have principal rays 506 a, 510 apropagating approximately parallel to each other, the downstreamintensity distribution becomes robust against potential failure ofupstream equipment. For example, should an intermediate beam fail duringuse due to a faulty diode or optical fiber, the uniformity of theintensity distribution at the work surface is not significantly altered.

FIG. 6 illustrates a representative exposure apparatus 600. Opticalpower from a plurality of fiber coupled laser diode modules 602 iscoupled to a beam shaping optical system 610 such as discussed abovewith one or more optical fibers 608. The beam shaping optical system 610provides a uniform optical beam with a selected beam shape, andtypically a rectangular beam having intensity variations of less thanabout 10%, 5%, 4%, or less across the beam. The laser diode modules 602are generally coupled to a cooling system 604 and a power/control system606. The uniform beam from the optical system 610 is directed to a mask612, and a projection lens 614 images the mask 612 onto a work piece616. Typically, the rectangular beam can provide optical powers of up to2-3 kW and beam intensities of 5-10 kW/cm². In other embodiments, suchas for annealing for example, beam intensities may be significantlyhigher, such as between 50 and 100 kW/cm². Reflected optical power fromthe mask 612 can be directed to a beam dump 620 with one or more opticalelements 618. Typically, the beam dump 620 and the optical elements 618are oriented so as to eliminate or reduce reflections back to the mask612.

As shown in FIG. 10, in some embodiments, the beam shaping system 610 isdisposed in a housing 630 separate from the fiber coupled laser modules602 and a harness 632 securing bendable optical fibers 608 flexiblyconnects the modules 602 and system 610. In this way, the system 610 isfree to translate with respect to modules 602 for effective surfaceworking, such as, for example, controlled annealing, cutting, scribing,or marking of a substrate. For example, the system 610 may be mounted toa gantry (not shown) that can move or track in order to bring the system610 to a different position so that a separate portion of a target worksurface 634 may be irradiated.

While a beam interleaver having rectangular segments is convenient,other configuration are possible. With reference to FIG. 7, a beaminterleaver 700 includes a plurality of circular (or oval) reflectiveregions 704 on a surface 706 of a transmissive substrate 708. Thesurface 706 of the transmissive substrate 708 can be provided withanti-reflections coatings outside of the regions 704 so as to enhancebeam transmittance. An anti-reflection coating can also be provided on asurface opposite the surface 706. Alternatively, the regions 704 can beconfigured as transmissive regions with anti-reflection coatings, andthe remainder of the surface 706 can be provided with a reflectivecoating.

While a folded, reflective optical system can be used, optical systemsusing refractive optical elements can be used as well. With reference toFIG. 8, an illumination optical system 800 includes optical fiber inputs802, 803, 804 which secured in respective ferrules 806, 807, 808.Optical radiation from the fiber inputs 802, 803, 804 is directed tobeam forming optics 810, 811, 812 to produce beams 814, 815, 816,respectively that propagate along an optical axis 801. A first lens 818is situated on the axis 801 and directs the beams 814, 815, 816 to asecond lens 826 along axes 820, 801, 822, respectively. Upon exiting thefirst lens 818, the beams 814, 815, 816 are converging towards thesecond lens 826 which then directs the beam into a light pipe 830. Asshown in FIG. 8, the second lens 826 receives the converging beam 816and focuses the beam at a beam focus 832. The beam focus 832 cancorrespond to a minimum beam size along both the x-direction and they-direction, but in some examples the beam focus 832 is a line focuscorresponding to a beam that is focused in one direction but not in anorthogonal direction. For purposes of illustration, perimeter rays 832a, 832 b are shown as intersecting on the axis 822. Similar focusedbeams 833, 834 corresponding to the input beams 814, 815, respectively,are also formed. The focused beams 832, 833, 834 are situated on a focalline or focal plane 836 that can be within or exterior to the light pipe830. The focal plane 836 can also have a non-planar shape depending onthe optical elements selected for use. For convenience, refraction at afrontal surface 831 of the light pipe 830 is not shown.

The focused beams 832, 834 generally propagate in the light pipe 830within a common range of propagation angles after reflection by lightpipe sidewalls 838, 840. Additional input beams can be provided so thatinput beams can overlap or be situated close to each other with gaps of0.1, 0.2, 0.5, 1.0, 2.0 or more times a beam radius. A beam interleavercan be provided for this purpose. In FIG. 8, the input beams aresituated in a linear array, and focusing only in a single plane isshown. The first lens 818 and the second lens 826 can be cylindricallenses having spheric or aspheric curvatures along one axis and lackingcurvature along an orthogonal axis. In other examples, two dimensionalbeam arrays can be used, and the first lens 818 and the second lens 826are not cylindrical lenses. In other examples, these lenses can havediffering spheric or aspheric curvatures along orthogonal directions.

Also seen in FIG. 8, before entering second lens 826, representativebeams 814, 815, 816 converge on a focus 825. The second lens 826 maythen be a telecentric lens such that the principal rays of beams 820,801, 822 propagate past the second lens 826 approximately parallel toeach other, and also past the second lens 826 the beams 820, 801, 822converge on a respective beam focus 832, 833, 834 in focal plane 836.Focal plane 836 can also have curvature as well, however as shown inFIG. 8 the focus 836 is planar. Second lens 826 may also be a fouriertransform lens resulting in the telecentric imaging of therepresentative beams 820, 801, 822 into the light pipe 830. The focallength of the fourier transform lens 826 determines the size of theimage and divergence of light form each point on the image. Since theprincipal rays of the beams 820, 801, 822 are parallel, downstreamoptics, such as for example projection lens 614, operate independentlyof which fiber coupled light source contains power. Thus, shouldparticular fiber coupled light sources lose power, the intensitydistribution exiting the light pipe 830 remains uniform and insensitiveto the power loss due to the telecentric imaging of the input beams 820,801, 822.

The first lens 818 and the second lens 826 are shown as single element,refractive lenses. Compound or multi-element lenses can be used, andholographic, Fresnel, or other optical elements can be used. Forexample, the first lens 818 can be segmented to provide suitablerefraction of the input beam to the second lens 826, without convergingthe input beams. Such refraction is provided so that the second lens 826receives substantially all (greater than at least 80%) of the opticalpower in the input beams.

The frontal surface 831 of the light pipe can have a square,rectangular, or other shape. A two dimensional square array of inputbeams can be selected for use with a square light pipe frontal surface,and a linear or rectangular array used with a rectangular frontalsurface. The light pipe 830 can be tapered in one or more directions toprovide an output surface that has a larger or smaller area than thefrontal surface 831, or to have a different shape or aspect ratio thanthe frontal surface 831. As shown in FIG. 8, the light pipe 830 has aheight H in the y-direction so that focused input beams from the secondlens 826 are captured in the light pipe 830.

FIG. 9 is a view of the optical system of FIG. 8 in an xz-plane andcontaining the axis 801. The beam 815 propagates along the axis 801through the first lens 818 and the second lens 826 without appreciabledivergence in the xz-plane. The beam forming optics 811 is configured toproduce a suitable beam width W that irradiates a selected portion ofthe light pipe frontal surface 831. As shown in FIG. 9, the beamdivergence is selected so that the beam propagates within the light pipe830 without substantial interaction with or reflection from the lightpipe side walls 848, 850. It will be apparent light pipe x-axis widthcan be selected to provide such reflections. Beam width in thex-direction at an output surface 861 is substantially the same as at thefrontal surface 831. The beam 815 is illustrated as substantiallycollimated in FIG. 9 and having a substantially constant beam width W.Typically, beam divergence in the x-direction can be selected so that inthe x-direction the beam width does not change substantially as the beampropagates in the light pipe 830. In the view of FIG. 9, the beams 814,816 of FIG. 9 are not shown, but are similar to the beam 815. As notedabove, in other examples, beam propagation and shaping in the xz-planeand the yz-plane are substantially the same.

Typically in systems such as described above, some radiation isreflected from work surfaces or other surfaces, such as a mask, and as aresult is not used in process. Such radiation can be captured with oneor more beam dump that can be integrated to collect waste radiation. Thebeam dump generally includes an absorbent material, generally a metal,that is situated so as to receive and absorb waste radiation. The beamdump conducts the heat generated in response to waste radiationabsorption away from the irradiation system. The heat can be dispersedwith air-cooling or water-cooling. Optics can be placed before the beamdump to collect the reflected radiation and direct it toward the beamdump, allowing flexibility in beam dump placement and size.

It is thought that the present invention and many of the attendantadvantages thereof will be understood from the foregoing description andit will be apparent that various changes may be made in the partsthereof without departing from the spirit and scope of the invention orsacrificing all of its material advantages, the forms hereinbeforedescribed being merely exemplary embodiments thereof.

The systems, apparatus, and methods described herein should not beconstrued as limiting in any way. Instead, the present disclosure isdirected toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved. Any theories of operation are to facilitateexplanation, but the disclosed systems, methods, and apparatus are notlimited to such theories of operation.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “produce” and “provide” todescribe the disclosed methods. These terms are high-level abstractionsof the actual operations that are performed. The actual operations thatcorrespond to these terms will vary depending on the particularimplementation and are readily discernible by one of ordinary skill inthe art.

What is claimed is:
 1. A system for homogenizing the optical intensityprofile of light, comprising: a plurality of fiber coupled lightsources, for emitting fiber output beams from corresponding fiber outputends thereof, said fiber output ends including a first set of said fiberoutput ends displaced from each other and arranged to emit acorresponding first set of said fiber output beams in a first directionand a second set of said fiber output ends displaced from each other andarranged to emit a corresponding second set of said fiber output beamsin a second direction, each of said fiber output beams having aprincipal ray; a light pipe optically coupled to said fiber output beamsfor producing a light pipe output beam; an interleaver configured tointersect said first and second sets of fiber output beams and directsaid principal rays thereof into a common direction in relation to anoptical axis; and one or more optical elements situated along saidoptical axis between said interleaver and said light pipe, said one ormore optical elements including a telecentric lens for telecentricallyimaging said fiber output beams into said light pipe.
 2. The system ofclaim 1, wherein said light pipe output beam has a homogenized intensityprofile along at least one axis.
 3. The system of claim 1, wherein saidlight pipe includes a core and a cladding comprised of substantiallytransparent materials wherein said core material has a refractive indexsufficiently greater than said cladding material so as to cause totalinternal reflection of said fiber output beams.
 4. The system of claim1, wherein said light pipe is made of a substantially transparentmaterial, said material having an index of refraction with a gradedprofile being higher near the center of the light pipe.
 5. The system ofclaim 1, wherein said light pipe is made of a substantially transparentset of materials having differing indices of refraction so as to createsmall reflections.
 6. The system of claim 1, wherein said light pipe hasa hollow interior and at least two opposing mirror sidewalls.
 7. Thesystem of claim 1, wherein said light pipe has a substantially round,square, or rectangular configuration.
 8. The system of claim 1, whereinsaid light pipe output beam has a homogenized intensity profile alongtwo perpendicular axes.
 9. The system of claim 1, wherein the light pipeis folded in one or more directions so as to increase the path length ofor change the direction of light propagating therethrough.
 10. Thesystem of claim 1, wherein said light pipe is tapered.
 11. The system ofclaim 1, wherein each of said fiber coupled light sources includes atleast two laser diodes coupled to a multimode fiber.
 12. The system ofclaim 1, wherein said light pipe includes a solid transparent substratethat defines a propagation volume having a rectangular cross section ofwidth W and height H.
 13. The system of claim 1, wherein said light pipeis situated so as to multiply reflect said fiber output beamspropagating therethrough according to the numerical aperture of each ofsaid beams.
 14. The system of claim 1, wherein said light pipe includesa frontal surface of height H configured to receive said fiber outputbeams, and at least two exterior surfaces configured to multiply reflectsaid fiber output beams from an input portion of said frontal surface toan output portion of said frontal surface so as to produce an outputradiation flux.
 15. The system of claim 14, further comprising a beamprocessing lens configured to produce a process beam based on saidoutput radiation flux.
 16. The system of claim 1, further comprising: atarget surface situated to receive said light pipe output beam; and abeam dump situated to receive and absorb radiation reflected from saidtarget surface, and disperse heat generated by said absorbed radiation.17. The system of claim 16, wherein said beam dump includes awater-based cooling system or an air-based cooling system.
 18. Thesystem of claim 1, wherein said light pipe output beam is opticallycoupled to a work piece.
 19. The system of claim 18, further comprisingprojection optics which optically couple said light pipe output beam toa work piece.
 20. The system of claim 19, further comprising a housingin which said light pipe and said projection optics are disposed, saidhousing being mounted to a gantry.
 21. The system of claim 1, whereineach of said fiber coupled light sources include at least onesemiconductor laser optically coupled to a multimode fiber.
 22. Thesystem of claim 21, wherein said semiconductor lasers emit light between700 nm and 1100 nm.
 23. The system of claim 22, wherein saidsemiconductor lasers emit light between 800 nm and 1000 nm.
 24. Thesystem of claim 1 wherein said common direction is a common plane. 25.The system of claim 24 wherein said principal rays are parallel to,divergent from, or convergent upon each other in said common plane. 26.The system of claim 24, wherein said interleaver transmits said firstset of fiber output beams into said common plane and reflects saidsecond set of fiber output beams into said common plane.
 27. The systemof claim 26 wherein said principal rays of said transmitted beams aresituated adjacent to and parallel with each other and of said reflectedbeams are situated adjacent to and parallel with each other.
 28. Asystem for homogenizing the optical intensity profile of light,comprising: a plurality of fiber coupled light sources, for emittingfiber output beams from corresponding fiber output ends thereof; saidfiber output ends including a first set of said fiber output ends aredisplaced from each other and arranged to emit a corresponding first setof said fiber output beams in a first direction and wherein a second setof said fiber output ends are displaced from each other and arranged toemit a corresponding second set of said fiber output beams in a seconddirection, each of said fiber output beams having a principal ray alight pipe optically coupled to said fiber output beams for producing alight pipe output beam; an interleaver configured to intersect saidfirst and second sets of fiber output beams and direct said principalrays thereof into a common direction in relation to an optical axis; andone or more optical elements situated along said optical axis betweensaid interleaver and said light pipe, said one or more optical elementsincluding a first optical element configured to receive each of saidfiber output beams at a corresponding portion of said first opticalelement and to direct said principal rays thereof towards a convergencein said common direction at an intersection of said optical axis, saidone or more optical elements also including a second optical elementsituated after a focus of said first optical element, and configured toreceive said fiber output beams therefrom and to image said principalrays after said second optical element approximately parallel to saidoptical axis; wherein said second optical element is a telecentric lensfor telecentrically imaging said fiber output beams into said lightpipe.